We examine the quenching reaction $\text{Rb}\left({}^{2}S\right)+\text{NH}\left({}^1\Delta \right)\to \text{Rb}\left({{}^{2}P}_{1/2}\right)+\text{NH}\left(X{{}^3\Sigma }^{-}\right)$. This reaction may be utilized to produce ground-state NH molecules for studies of ultracold physics or for other purposes and is interesting in that it involves initial and final states that are nearly degenerate. This near degeneracy is expected to lead to a large reaction rate. We examine this system using ab initio quantum chemistry calculations and scattering calculations, which include spin-orbit effects, and find that the reaction rate is large and, in fact, approaches the quantum-mechanical unitarity limit. We discuss the prospects for an experimental examination of this system.

High resolution angle-resolved photoelectron spectra from Na atoms laser excited and aligned in the ${\text{Na}}^{\ast }$ $2p^{6}3p{{}^{2}P}_{3/2}$ state are investigated experimentally and theoretically in the region of the ${\text{Na}}^{+}$ $2p^{5}3p$ manifold. A prominent influence of the alignment on the relative line intensities is observed. The measured linear alignment dichroism is in good agreement with the theoretical results obtained in the multiconfigurational Dirac-Fock approximation as well as in a generalized geometrical model, which is extended to the description of angular distributions of photoelectrons from polarized atoms.

We consider the stability of an ultracold trapped Bose-Einstein condensate near a Feshbach resonance. Using a modified Gross-Pitaevskii equation that includes higher-order terms and a multichannel model of Feshbach resonances, we find regions where stability can be enhanced or suppressed around experimentally measured resonances. We suggest a number of ways to probe the stability diagram. Using scattering length zero crossings huge deviations are found for the critical particle number. Effects are enhanced for narrow resonances or tighter traps. Macroscopic tunneling of the condensate is another possible probe for higher-order interactions; however, to see this requires very narrow resonances or very small particle numbers.

Increase in the cutoff value in the high-order harmonics generation process is demonstrated for a special case of the driving field composed of several harmonics of a given frequency. It is shown that a moderate, of the order of 20%, increase in the cutoff value can be achieved. This result possibly constitutes an upper limit for the increase in the cutoff value, attainable for a class of the waveforms considered in the paper.

Within the numerically exact solution to the Dicke model proposed previously, we study the quantum criticality in terms of the ground-state (GS) energy, fidelity, and the order parameter. The finite size scaling analysis for the average fidelity susceptibility (FS) and second derivative of GS energy are performed. The correlation length exponent is obtained to be $\nu =2/3$, which is the same as that in Lipkin-Meshkov-Glick model obtained previously, suggesting the same universality. It is observed that average FS and second derivative of GS energy show similar critical behavior, demonstrating the intrinsic relation in the Dicke model. The scaling behavior for the order parameter and the singular part of the GS energy at the critical point are also analyzed and the obtained exponents are consistent with the previous scaling hypothesis in $1/N$ expansion scheme.

Based on the assumption of partial separability, we derive Bell-type inequalities for $N$ $d$-dimensional (qudit) systems, which can detect experimentally genuine multipartite entanglement that cannot be reduced to mixtures of states in which a smaller number of particles are entangled. We also introduce the concept “resolution” to measure the strength of these inequalities to distinguish full entanglement from partial entanglement when white noise is added to the system.

We derive an explicit analytic estimate for the entanglement of a large class of bipartite quantum states, which extends into bound entanglement regions. This is done by using an efficiently computable concurrence lower bound, which is further employed to numerically construct a volume of $3\times 3$ bound entangled states.

We show that the Fano representation leads to a particularly simple and appealing form of the quantum process tomography matrix ${\chi }_F$, in that the matrix ${\chi }_F$ is real, the number of matrix elements is exactly equal to the number of free parameters required for the complete characterization of a quantum operation, and these matrix elements are directly related to evolution of the expectation values of the system’s polarization measurements. These facts are illustrated in the examples of one- and two-qubit quantum noise channels.

We show that several classes of mixed quantum states in finite-dimensional Hilbert spaces which can be characterized as being, in some respect, “most classical” can be described and analyzed in a unified way. Among the states we consider are separable states of distinguishable particles, uncorrelated states of indistinguishable fermions and bosons, as well as mixed spin states decomposable into probabilistic mixtures of pure coherent states. The latter was the subject of the recent paper by Giraud et al. [Phys. Rev. A 78, 042112 (2008)], who showed that in the lowest-dimensional nontrivial case of spin 1, each such state can be decomposed into a mixture of eight pure states. Using our method, we prove that in fact four pure states always suffice.

We calculate the relativistic corrections of relative order ${\left(Z\alpha \right)}^2$ to the two-photon decay rate of higher excited $S$ and $D$ states in ionic atomic systems, and we also evaluate the leading radiative corrections of relative order $\alpha {\left(Z\alpha \right)}^2\text{ln}\left[{\left(Z\alpha \right)}^{-2}\right]$. We thus complete the theory of the two-photon decay rates up to relative order ${\alpha }^3\text{ln}\left(\alpha \right)$. An approach inspired by nonrelativistic quantum electrodynamics is used. We find that the corrections of relative order ${\left(Z\alpha \right)}^2$ to the two-photon decay are given by the Zitterbewegung, by the spin-orbit coupling and by relativistic corrections to the electron mass, and by quadrupole interactions. We show that all corrections are separately gauge invariant with respect to a “hybrid” transformation from velocity to length gauge, where the gauge transformation of the wave function is neglected. The corrections are evaluated for the two-photon decay from $2S$, $3S$, $3D$, and $4S$ states in one-electron (hydrogenlike) systems, with $1S$ and $2S$ final states.

Proton and antiproton collisions with atomic hydrogen are investigated using the atomic-orbital close-coupling method. After a suitable transformation, the method leads to coupled three-dimensional momentum-space integral equations for the half-off-shell scattering amplitudes. These equations are further reduced to two-dimensional ones using the symmetry properties of the transition amplitudes. The resulting equations are solved directly without partial-wave expansion. The total and differential cross sections for electron transfer in proton collisions with the ground state of atomic hydrogen are calculated. The contribution of off-shell effects is fully taken into account and shown to be significant. We find that the off-shell effects can both increase or decrease the cross sections substantially depending on energy. At high energies as much as a half of the total electron transfer cross section comes from the off-shell effects. This contradicts classical and iterative estimates which predict the off-shell effects to be small. The significance of the off-shell effects in elastic scattering of protons falls with increasing energy to the estimated levels. The calculated cross section results agree well with experiment over a wide energy range. The total and differential cross sections for elastic scattering of antiprotons are also calculated and compared with the corresponding results for protons. Above 200 keV there is practically no difference between the cross sections for scattering of protons or antiprotons. The off-shell effects for elastic scattering of antiprotons are generally smaller than those for scattering of protons.

Time-dependent close-coupling calculations of the ionization and excitation cross section for antiproton collisions with molecular hydrogen ions are performed in an impact energy range from 0.5 keV to 10 MeV. The Born-Oppenheimer and Franck-Condon approximations as well as the impact parameter method are applied in order to describe the target molecule and the collision process. It is shown that three perpendicular orientations of the molecular axis with respect to the trajectory are sufficient to accurately reproduce the ionization cross section calculated by Sakimoto [Phys. Rev. A 71, 062704 (2005)] reducing the numerical effort drastically. The independent-event model is employed to approximate the cross section for double ionization and ${\text{H}}^{+}$ production in antiproton collisions with ${\text{H}}_2$.

We analyze the thermal Casimir-Polder potential experienced by a ground-state molecule in a planar cavity and investigate the prospects for using such a setup for molecular guiding. The resonant atom-field interaction associated with this nonequilibrium situation manifests itself in oscillating standing-wave components of the potential. While the respective potential wells are normally too shallow to be useful, they may be amplified by a highly reflecting cavity whose width equals a half-integer multiple of a particular molecular transition frequency. We find that with an ideal choice of molecule and the use of a cavity bounded by Bragg mirrors of ultrahigh reflectivity, it may be possible to boost the potential by up to two orders of magnitude. We analytically derive the scaling of the potential depth as a function of reflectivity and analyze how it varies with temperature and molecular properties. It is also shown how the potential depth decreases for standing waves with a larger number of nodes. Finally, we investigate the lifetime of the molecular ground state in a thermal environment and find that it is not greatly influenced by the cavity and remains in the order of several seconds.

We report the study of the optical and mechanical properties of high-$Q$ fused silica microtoroidal resonators at cryogenic temperatures (down to 1.6 K). A thermally induced optical multistability is observed and theoretically described, originating from the reverse thermally induced optical frequency shift. Moreover the influence of structural defect states (two level fluctuators) on their mechanical properties is observed and probed at an unprecedentedly achieved low phonon number. The resulting implications for cavity optomechanics and studies of mechanical decoherence are also discussed.

We discuss the behavior of quantum and classical pairwise correlations in critical systems, with the quantumness of the correlations measured by the quantum discord. We analytically derive these correlations for general real density matrices displaying $Z_2$ symmetry. As an illustration, we analyze both the $XXZ$ and the transverse field Ising models. Finite size as well as infinite chains are investigated and the quantum criticality is discussed. Moreover, we identify the spin functions that govern the correlations. As a further example, we also consider correlations in the Hartree-Fock ground state of the Lipkin-Meshkov-Glick model. It is then shown that both classical correlation and quantum discord exhibit signatures of the quantum phase transitions.

The entanglement properties of non-Gaussian states are investigated, which are obtained by performing the photon addition, photon subtraction, photon-addition-then-subtraction, and photon-subtraction-then-addition operations on the two-mode squeezed vacuum state. We show that the partial von Neumann entropy of all the resulting states is greater than that of the original squeezed state, but only the photon-subtracted states and the photon-added-then-subtracted states have the stronger Einstein-Podolsky-Rosen correlation than the original squeezed state. Quantum teleportation of Braunstein and Kimble protocol is studied for coherent states, squeezed states, and mixed Gaussian states with the non-Gaussian entangled resources. For all the states to be teleported, the fidelity with the photon-subtracted and the photon-added-then-subtracted entangled resources is higher than that with the two-mode squeezed vacuum resource. Based on Bures fidelity, we find that quantum teleportation for mixed and classical single-mode Gaussian states is more faithful than for single-mode Gaussian states with high purity and nonclassicality.

We consider a one-dimensional spin chain for which the ground state is the cluster state, capable of functioning as a quantum computational wire when subjected to local adaptive measurements of individual qubits, and investigate the robustness of this property to local and coupled (Ising-type) perturbations. We investigate the ground state both by identifying suitable correlation functions as order parameters, as well as numerically using a variational method based on matrix product states. We find that the model retains an infinite localizable entanglement length for Ising and local fields up to a quantum phase transition, but that the resulting entangled state is not simply characterized by a Pauli correction based on the measurement results.

A semiclassical model is developed to investigate the atomic nonsequential double-ionization process in elliptically polarized intense laser field. First, the ellipticity dependence of the ion yield of ${\text{Ne}}^{2+}$ is calculated and a good agreement with the experiment observation is found. Second, the frequency dependence of the ratio of ${\text{Ne}}^{2+}:{\text{Ne}}^{+}$ is investigated for fields with different ellipticities. In the high-frequency regime, the ratio increases rapidly with increasing wavelength and is not dependent on the ellipticity. However, the ratio reaches maximum which decreases with increasing ellipticity and decreases with wavelength in the long-wavelength regime.

Rubidium atoms prepared by evaporative cooling in an optical dipole trap are used in Stern-Gerlach type experiments. The analysis of the magnetic state distribution in the trap and during free fall demonstrates the possibility of ejecting all atoms with $m_F\ne 0$ from the optical dipole trap. This is achieved by applying an appropriately located inhomogeneous magnetic field. We investigate the dynamics of this cleaning process, and record the temporal history of atom positions under the combined action of magnetic field and dipole-trap potential. The experimental findings are fully supported by realistic numerical simulations of the atomic dynamics. We show that analysis of the ejected atoms provides a means for nondestructive thermometry of a trapped atom cloud.

In this paper we study the formation and dynamics of self-propelled cavity solitons (CSs) in a model for vertical-cavity surface-emitting lasers (VCSELs) subjected to external frequency-selective feedback and build their bifurcation diagram for the case where carrier dynamics is eliminated. For low pump currents, we find that they emerge from the modulational instability point of the trivial solution, where traveling waves with a critical wave number are formed. For large currents, the branch of self-propelled solitons merges with the branch of resting solitons via a pitchfork bifurcation. We also show that a feedback phase variation of $\pm 2\pi$ can transform a CS (whether resting or moving) into a different one associated to an adjacent longitudinal external cavity mode. Finally, we investigate the influence of the carrier dynamics, relevant for VCSELs. We find and analyze qualitative changes in the stability properties of resting CSs when increasing the carrier relaxation time. In addition to a drifting instability of resting CSs, a distinctive kind of instability appears for certain ranges of carrier lifetime, leading to a swinging motion of the CS center position. Furthermore, for carrier relaxation times typical of VCSELs the system can display multistability of CSs.